Researchers found a 38 percent decrease in the average probability of conception in a given menstrual cycle among women who reported severe depressive symptoms, compared to those with no or low symptoms.

The results were similar, regardless of whether the women were on psychotropic medications, they said.

Despite associations in prior studies between infertility and the use of antidepressants, antipsychotics or mood stabilisers among already infertile women, current use of psychotropic medications did not appear to harm the probability of conception, said Yael Nillni from Boston University in the US.

"Our findings suggest that moderate to severe depressive symptoms, regardless of current psychotropic medication treatment, may delay conception," said Nillni.

Depression has been associated with dysregulation of the hypothalamic-pituitary-adrenal axis, which may influence the menstrual cycle and affect the ability to conceive, researchers said.

They studied more than 2,100 female pregnancy planners. Participants were asked to report their current depressive symptoms and psychotropic medication use, among many other factors.

Overall, 22 percent reported a clinical diagnosis of depression in their medical histories, while 17.2 percent were former users of psychotropic medication, and 10.3 percent were current users of psychotropic drugs, researchers said.

They also found that current use of benzodiazepines - sedatives used to treat anxiety and other disorders – was associated with a decrease in pregnancy.

Women who were formerly treated with a class of antidepressants known as SSRIs (selective serotonin reuptake inhibitors) had improved chances of conception, regardless of depressive symptom severity, researchers said.

The findings were published in the American Journal of Obstetrics and Gynecology.